In conventional tape recorders, a signal of interest is recorded on the tape as the tape is moved by the tape transport from a supply reel to a takeup reel. Some means is normally included to indicate to the operator the location of tape (commonly referred to as "footage") which is adjacent the read/record heads, or simply "transducer". Two particular locations are of interest to the operator concerning the data recorded. These are the Beginning of Data (BOD) and End of Data (EOD) footage locations. Typically, the BOD and EOD locations are recorded either on a voice track on the same tape by an operator during recording, or noted in a written log by the operator. He may note a specific event that occurred along with a notation of the footage indicator at the time the event occurred. Normally, all other events of interest are referenced to a particular noted event. In some systems, the operator may have the option of resetting the footage counter to zero at a particular event, thereby referencing all subsequent events relative to zero footage. There is normally some ambiguity in the actual BOD location thus determined because the operator may actually run a hundred or more feet of tape through the machine before beginning to record. This is done in the case of valuable data to insure that the tape on which the recording is made is not damaged.
During playback or analysis, the operator may not know where the footage counter had been set to zero or recording begun. Rather, he must first recognize and identify the event from which reference is made, and then he can correlate the event either with the written log or a recording on the voice track. In this manner, he knows where other events are located by reference to the footage indicator and log. However, it may be necessary for him to calculate where other data events are located on the same tape. For example, if he knows that a reference event occurs at twenty feet on the recorded tape, and he is looking for an event at four hundred feet, when he loads the tape for playback, and identifies the first event, his footage indicator may indicate forty feet, thereby requiring a calculation before he can locate the event of interest. These calculations can introduce error, and they are always an inconvenience.
One mode of operation using the BOD and EOD points is commonly referred to as "shuttle". Typically, the BOD and EOD locations are identified by conductive or reflective markers, or the locations are specified by advancing the tape of each location and setting an electromechanical counter at the two locations. When the traditional shuttle mode of operation is entered, the transport moves the tape forward at the desired speed reproducing the signal recorded on the tape to the EOD point, and then moves the tape in fast reverse to BOD. This process is repeated until the operator deactuates or stops the transport. As described below, the present invention adds flexibility by permitting the user to enter other commands which will be executed at footage locations such as BOD and EOD.
Two other parameters useful in conventional tape recorders are Beginning of Tape (BOT) and End of Tape (EOT). These parameters are normally not defined by specific footage locations, as with BOD and EOD. Rather, mechanical follower arms engaging the tape pack, conductive or reflective markers, transparent leaders, or light source/photodetector combinations are used to keep track of the amount of tape on the reel being emptied by transport motion.
The EOT parameter is used in emptying the source reel when the transport is operating in a forward direction, and BOT is used when rewinding the tape from the takeup reel onto the source reel. One disadvantage of prior tape recorders is that the EOT and BOT parameters are not easily changed or re-set. That is to say, in the case of conductive or reflective spots or transparent leaders, the locations had to be first identified and then changed. If one of these parameters were identified by removing the magnetic coating with solvent, changing is even more difficult. In other systems, mechanical adjustments are required for changing the identification of these parameters.
The control apparatus of the present invention includes a Central Processor Unit (CPU) and a Control Panel having data entry switches, mode selection switches, speed selection switches, a multiposition function select switch, and other controls and a display which communicates with the CPU. The control panel enables the operator to enter commands as well as data into the system. Commands are recognized by the CPU and executed in controlling the tape transport at predetermined footages (such as BOD or EOD) as well as at predetermined parameter definitions (such as at BOT or EOT). In defining BOT and EOT, the CPU accumulates pulses from a capstan transducer representative of linear tape footage for distance that has been transported. At the same time, the CPU uses pulses from a transducer associated with the supply reel motor and the takeup reel motor which are representative of angular displacement of the supply reel and takeup reel respectively. A ratio of capstan pulses to either supply reel or takeup reel pulses is determined. This ratio is a pure number which is representative of the diameter of remaining tape pack. It is independent of operating speed, and it decreases monotonically as a reel is being emptied. A predetermined number is thus used to define BOT and EOT; and it is very easily entered or changed by the operator, using the data entry switches, in combination with the function switch on the control panel.
The present invention also permits the operator to enter commands (referred to as User Commands) at any of the locations BOD, EOD, BOT or EOT. These commands are stored in the CPU and executed when the associated location is reached or parameter defined, to control the transport. Thus, the number of commands are available for entry by the user (again, using the function select switch and data entry switches on the control panel) either at predetermined footage locations on the tape or in accordance with other parameter definitions. Thus, the operator is not limited to the traditional shuttle mode of operation--rather, he can program any number of modes of operation. For example, at EOD, he can program the control mechanism such that the transport will stop, go into a reverse record mode of operation or transfer recording to another machine by entering a single command at the control panel. In the illustrated embodiment, this command is a single digit number. At BOD, he can cause the machine to go into forward record mode of operation--again, by entering a single command at that location. To enter these commands, the tape need not be at the location at which it is desired to execute the command because the command is stored in the CPU, and the CPU keeps an updated and accurate record of footage as well as the ratio of capstan to reel angular displacement described above. Thus, when the particular footage location or parameter definition is identified by the CPU, the command is brought up and executed.
Another advantage of the pesent invention is that the footage counter may be set by the operator to any desired footage indication. In other words, rather than being limited to resetting the footage counter to zero, the operator may, upon identification of a specific event such as that which defines BOD, set the footage counter to the number indicated either on the voice track of the recording or in a written log. This enables the operator during a playback of a tape to obtain exact correlation with the footage indicator during a previous recording. The new indication, because it is stored in memory in the CPU, may be entered through the same data entry switches and function switch which are used for the entry of other data as well as commands.
The operator may set the speed of the transport by depressing any one of ten separate speed control pushbuttons at the control panel. However, actual speed is controlled by the CPU, so that programmed speed control is possible. This is useful, for example, when an operator may be emptying a reel in the slew mode. It may be undesirable to permit the end portion of a tape to pass through the transport at the slew rate. The CPU, recognizing that the transport is operating in the slew mode, will identify EOT and automatically cause the transport to slow down to a lower speed. Further, because of the particular tape transport mechanism with which it is desirable to employ this invention, it is advantageous to program the speed of the capstan during start up and motion reversal. Specifically, as is more fully disclosed in the copending application of Prozzo, et al, Ser. No. 788,443, filed Apr. 18, 1977 for TAPE TRANSPORT, which is co-owned, the transport includes two drums providing tape-carrying surfaces which are closely spaced realtive to the transducer in a short-loop configuration. These drums are surface-driven by a single capstan which has a polyurethane peripheral drive surface. Because this material has "memory", it is undesirable to engage the capstan with the drums while the capstan is stopped. The CPU during start up at a desired speed, first stores the desired speed, and transmits a predetermined or programmed speed to the capstan. After the capstan has achieved this speed, the CPU transmits signals that cause the drums to engage the capstan at either a read position (in which the tape is in operative relation with the transducer) or a transport position (in which the tape does not engage the transducer), and then transmits signals to the transport which are representative of the desired operating speed. Other features and advantages of the present invention accrue in the use of the preferred transport mechanism described in the Prozzo, et al application, identified above.
Thus, the present invention provides a tape control system in which the various functions performed by the tape transport, and the sequencing thereof, are implemented under command from a programmable data processor. This permits great flexibility in changing the response locations on tape or other response parameters, as well as in changing command functions at such locations. It also provides flexibility in the entry of data and the programmed speed control of the transport. Flexibility and adaptability are important characteristics in a laboratory tape recorder because of the wide variety of uses to which such an instrument is put.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.